And so, the pupils who have risen before dawn, catch a flight to Krakow for a journey that will reveal misery and cruelty almost beyond belief.

The first stop is the old cemetery, which translates as ‘place of life’.

It belonged to the original village in which 58 per cent of the population were Jewish.

“These people lived together, they respected each others holidays, they got along very well,” our educator, Emma Kinney, explained.

With sunlight dancing through the trees, it feels peaceful. But this is no escape from the horrors to follow – it is just a prelude.

“These graves were ripped up and used as paving stones during the Nazi occupation of Poland,” explained Emma. “When the war ended, one man made it his mission to replace them and so they were returned to the sacred ground, even if the headstones now mark the wrong graves.”

There is another lesson here, but it is not a history lesson: the tall iron gates we enter are usually kept locked for fear of anti-semitic attacks. Graffiti is common.

There is a phrase, repeated throughout the day, which sums up why these young people are being shown things they shouldn’t have to see: “If it can happen once, it can happen again”.

We move on to Auschwitz I, passing under the infamous gates that bear the slogan ‘Arbeit macht frei – Work brings freedom’.

Our guide, Ilona, is quietly spoken but sometimes her voice burns with anger, repeating a story she must have told hundreds of times.

“You must remember that the SS guards here were volunteers – no-one forced them to work here,” she said. The walls of Auschwitz I are lined with photographs of inmates and the dates of the arrival and their deaths. Only a few months separate the two.

As well as the Jews, around 64,000 Poles, 21,000 Sinti and Roma, 15,000 Soviet POWs and 12,000 victims from other groups were killed in Auschwitz-Birkenau.

One exhibit is a huge pile of empty containers of Zyklon B, the poison used in the gas chambers. “This way, they didn’t have to look people in the eye while they killed them,” said Ilona.

Another room contains a glass case full of human hair shaved off the women to be sold; the hair colours have hardly faded, plaits, hair combs and pins are still visible.

The students are solemn, wide-eyed and attentive but not visibly upset. “It will hit them later,” said Emma.

“Often, the adults get more upset because they ‘get it’ straight away.”

Auschwitz famously contains personal effects of those who were murdered: suitcases, glasses, clothing, shoes. But nothing prepares you for the scale of it: the piles of shoes, the precious dishes.

“You don’t take your best crockery if you think you’re going to die,” said Emma. “You don’t take your keys if you think you’ll never see your house again.”

The pupils make their way back on to the coach for the 3km journey to Auschwitz Birkenau – the place that brought Jews from across Europe, packed into wagons, to be sent to the work camp or the gas chambers.

The crematoria, where the bodies were burned, were destroyed by the Nazis when they realised they were about to lose the war but otherwise it has been kept much as it was found when liberated by the Red Army.

From the iconic watchtower, the remains of the murder factory stretch out before us. Every room tells a story of dignity being stripped away, health being stolen, humanity robbed.

It’s been a long day. “I am so tired but I feel I can’t really complain,” I heard more than one young person saying.

The last room is full of photographs of people in happier days. The pupils are urged to choose someone to remember – as a human being, not a victim.

The visit ended with a ceremony beside the ruined crematoria, where Rabbi Andrew Shaw addressed the young people.

As dusk fell and the evening air cooled, they took candles to lay along the railway track that brought so many to their deaths.

It is not a day they will ever forget.

The message they take away is clear: this happened, and if it can happen once it can happen again.